1. Field of the Invention
The present invention relates to a control apparatus for a hydraulically-operated vehicular transmission having a plurality of hydraulic engaging elements for selectively establishing a plurality of speed transmission trains (or speed stages). In this invention, the term xe2x80x9cvehicular transmissionxe2x80x9d means a transmission for use in a vehicle such as a motor vehicle.
2. Description of the Related Art
As this kind of control apparatus, there is known the following in Japanese Published Unexamined Patent Application No. 229179/1997. Namely, the control apparatus comprises a pair of linear solenoid valves, and switching means for switching oil passage connections into a state in which an oil pressure in a hydraulic engaging element for an arbitrary speed transmission train and an oil pressure in a hydraulic engaging element for a speed transmission train which is adjacent, as seen in an order of speed, to the arbitrary speed transmission train are controllable by the pair of linear solenoid valves. The switching means is controlled, at the time of speed changing, such that an oil pressure in an off-going hydraulic engaging element for a speed transmission train so far established and an oil pressure in an on-coming hydraulic engaging element for a speed transmission train to be established next which is adjacent, as seen in the order of speed, to the speed transmission train so far established become controllable by the pair of linear solenoid valves. (Note: The xe2x80x9coff-goingxe2x80x9d hydraulic engaging element is a hydraulic clutch which has so far been engaged but which is to be disengaged from now on and the xe2x80x9con-comingxe2x80x9d hydraulic engaging element means a hydraulic clutch which is going to be engaged from now on.) In addition, the pair of linear solenoid valves are controlled such that the oil pressure in the off-going hydraulic engaging element is lowered by one of the pair of linear solenoid valves, said one linear solenoid valve handling the off-going hydraulic engaging element, and that the oil pressure in the on-coming hydraulic engaging element is increased by the other of the pair of linear solenoid valves, said the other linear solenoid valve handling the on-coming hydraulic engaging element.
In the above-described conventional apparatus, the oil pressure in each of the on-coming and the off-going hydraulic engaging elements can be directly controlled by each of the linear solenoid valves. It is therefore advantageous in buffering or reducing a speed change shock.
In this conventional apparatus, however, it is only the two hydraulic engaging elements adjacent or next to each other as seen in the order of speed that can be controlled by the pair of linear solenoid valves. Therefore, in case a skipped speed change command (i.e., a command to change the transmission train by skipping one or more transmission trains), e.g., a command of downshifting from the 5th-speed transmission train to the 3rd-speed transmission train is issued, it is impossible to simultaneously control the oil pressures in the hydraulic engaging element for the 5th-speed transmission train and the oil pressure in the hydraulic engaging element for the 3rd-speed transmission train. As a solution, it is necessary, first, to control the oil pressures in the hydraulic engaging element for the 5th speed and in the hydraulic engaging element for the 4th-speed by the pair of linear solenoid valves to thereby downshift from the 5th-speed transmission train to the 4th-speed transmission train. It is, thereafter, necessary to control the oil pressures in the hydraulic engaging element for the 4th speed and in the hydraulic engaging element for the 3rd speed by the pair of linear solenoid valves to thereby downshift from the 4th-speed transmission train to the 3rd-speed transmission train. In this manner, it is possible with this conventional apparatus to perform the speed changing (or speed shifting) only one speed transmission train (or one speed stage) at a time. As a result, the speed change response to the skipped speed change command becomes poor.
In view of the above-described disadvantages, the present invention has an object of providing a control apparatus for a hydraulically-operated vehicular transmission in which the skipped speed changing can be smoothly performed with a good response.
In order to attain the above and other objects, the present invention is a control apparatus for a hydraulically-operated vehicular transmission having a plurality of hydraulic engaging elements for selectively estabilishing a plurality of speed transmission trains, said apparatus comprising: a pair of linear solenoid valves; switching means for switching oil passage connections into a state in which an oil pressure in a hydraulic engaging element for an arbitrary speed transmission train and an oil pressure in a hydraulic engaging element for a speed transmission train which is adjacent, as seen in an order of speed, to the arbitrary speed transmission train are controllable by the pair of linear solenoid valves; first control means for speed changing which controls the switching means at a time of speed changing such that an oil pressure in an off-going hydraulic engaging element for a speed transmission train so far established and an oil pressure in an on-coming hydraulic engaging element for a speed transmission train to be established next which is adjacent, as seen in the order of speed, to the speed transmission train so far established, become controllable by the pair of linear solenoid valves, the first control means also controlling the pair of linear solenoid valves such that the oil pressure in the off-going hydraulic engaging element is lowered by one of the pair of linear solenoid valves, said one linear solenoid valve handling the off-going hydraulic engaging element, and that the oil pressure in the on-coming hydraulic engaging element is increased by the other of the pair of linear solenoid valves, said the other linear solenoid valve handling the on-coming hydraulic engaging element; an accumulator connected to an oil passage which is in communication with a predetermined first speed transmission train; and second control means for speed changing which controls the switching means, at a time of speed changing from the first speed transmission train to a second speed transmission train which is not adjacent to the first speed transmission train as seen in the order of speed, such a) that the oil passage which is in communication with a hydraulic engaging element for the first speed transmission train is connected to an oil discharge passage, and b) that an oil pressure in a hydraulic engaging element for the second speed transmission train and an oil pressure in a hydraulic engaging element for a third speed transmission train which is adjacent to the second speed transmission train on a side near the first speed transmission train, as seen in the order of speed, are controllable by the pair of linear solenoid valves, the second control means also controlling the pair of liner solenoid valves such c) that the oil pressure in the hydraulic engaging element for the second speed transmission train is increased by one of the pair of liner solenoid valves, said one linear solenoid valve handling the hydraulic engaging element for the second speed transmission train, and d) that the oil pressure in the hydraulic engaging element for the third speed transmission train is kept to a state before the pressure increasing by the other of the pair of liner solenoid valves, said the other linear solenoid valve handling the hydraulic engaging element for the third speed transmission train. (Note: In this specification, xe2x80x9c1stxe2x80x9d, xe2x80x9c2ndxe2x80x9d, etc. as in xe2x80x9c1st-speed transmission trainxe2x80x9d, etc. are used in a true sense of numerical order, i.e., in the meaning of No. 1, No. 2, etc. On the other hand, xe2x80x9cfirst speedxe2x80x9d, xe2x80x9csecond speedxe2x80x9d, etc. as in xe2x80x9ca first speed transmission trainxe2x80x9d, etc. are used not in the true numerical order but in the sense as explained herein.)
According to the present invention, when a skipped speed change command is issued to change the speed from the first speed transmission train (5th speed transmission train in the embodiment to be described in more detail hereinafter) to the second speed transmission train (3rd speed transmission train or 2nd speed transmission train in the embodiment), the connections of the oil passages are switched to the state in which the oil pressure in the hydraulic engaging element for the second speed transmission train and the oil pressure in the hydraulic engaging element for the third speed transmission train (4th speed transmission train or 3rd speed transmission train in the embodiment) are controllable by the pair of linear solenoid valves. In this state, although the oil pressure in the hydraulic engaging element for the first speed transmission train can no longer be controlled by the linear solenoid valves, a sudden pressure decrease in the hydraulic engaging element for the first speed transmission train can be buffered by the accumulator. In conjunction with the pressure increase control of the oil pressure in the hydraulic engaging element for the second speed transmission train by one of the linear solenoid valves, the skipped speed changing can be provided at a good response without giving rise to large shocks.
Further, in the course of skipped speed changing from the first speed transmission train to the second speed transmission train, a speed change command from the second speed transmission train to the third speed transmission train will sometimes be issued due to a change in the depressed state of an accelerator pedal or the like. According to the present invention, during the skipped speed changing from the first speed transmission train to the second speed transmission train, the other of the pair of linear solenoid valves is kept ready for the increasing in the oil pressure in the hydraulic engaging element for the third speed transmission train. Therefore, when the speed change command to the third speed transmission train has been issued, the oil pressure in the hydraulic engaging element for the third speed transmission train can be quickly increased, and the speed changing to the third speed transmission train can thus be performed with a good response, resulting in a driver""s improved feeling at driving (or drivability).
At the time of speed changing from the first speed transmission train to a fourth speed transmission train (4th speed transmission train in the embodiment) which is adjacent to the first speed transmission train as seen in the order of speed, it is also possible to perform the following controls: namely, the connections of the oil passages are switched to the state in which the oil pressure in the hydraulic engaging element for the first speed transmission train and the oil pressure in the hydraulic engaging element for the fourth speed transmission train are controllable by both the linear solenoid valves; and the pressure decrease control of the oil pressure in the hydraulic engaging element for the first speed transmission train is performed by one of the linear solenoid valves, and the pressure increase control of the oil pressure in the hydraulic engaging element for the fourth speed transmission train is performed by the other of the linear solenoid valves, namely, the control by the above-described first control means for speed changing is performed. However, the pressure decrease characteristics of the hydraulic engaging element for the first speed transmission train will be subject to an effect by the accumulator. Therefore, the accumulator will be a possible cause for external perturbations in the pressure decrease control by the linear solenoid valves, thereby resulting in a speed change shock and a poor speed change response.
It is therefore preferable to provide the control apparatus with third control means for speed changing which controls the switching means, at a time of speed changing from the first speed transmission train to a fourth speed transmission train which is adjacent to the first speed transmission train, as seen in the order of speed, such e) that the oil passage which is in communication with the hydraulic engaging element for the first speed transmission train is connected to the oil discharge passage, f) that an oil pressure in a hydraulic engaging element for the fourth speed transmission train and an oil pressure in a hydraulic engaging element for a fifth speed transmission train which is adjacent to the fourth speed transmission train on a side away from the first speed transmission train, as seen in the order of speed, are controllable by the pair of linear solenoid valves, the third control means also controlling the pair of liner solenoid valves such g) that the oil pressure in the hydraulic engaging element for the fourth speed transmission train is increased by one of the pair of linear solenoid valves, said one linear solenoid valve handling the hydraulic engaging element for the fourth speed transmission train, and h) that the oil pressure in the hydraulic engaging element for the fifth speed transmission train is kept to a state before the pressure increasing by the other of the liner solenoid valves, said the other linear solenoid valve handling the hydraulic engaging element for the fifth speed transmission train. This arrangement has the following advantages. Namely, a smooth speed changing from the first speed transmission train to the fourth speed transmission train can be performed as a result of the function of buffering, by means of the accumulator, the pressure decrease of the oil pressure in the hydraulic engaging element for the first speed transmission train and as a result of the pressure increase control, by means of said one linear solenoid valve, of the oil pressure in the hydraulic engaging element for the fourth speed transmission train. When a speed change command to the fifth speed transmission train is issued in the course of the above-described speed changing, the oil pressure in the hydraulic engaging element for the fifth speed transmission train can be rapidly increased by said the other linear solenoid valve. As a result, the speed changing to the fifth speed transmission train can be performed with a good response.
In a state in which the pressurized oil is not sufficiently accumulated in the accumulator, the decrease in the oil pressure in the hydraulic engaging element for the first speed transmission train cannot be buffered effectively. As a solution, it is preferable to provide the control apparatus with detecting means for detecting an amount of accumulated oil in the accumulator; and prohibiting means for prohibiting the control by the second control means and the control by the third control means when the amount of accumulated oil as detected by the detecting means is discriminated to be below a predetermined value. In this manner, at the time of speed changing from the first speed transmission train when sufficient pressurized oil has not been accumulated in the accumulator, the control by means of the above-described first control means for speed changing is performed. Thus, the pressure decrease of the oil pressure in the hydraulic engaging element for the first speed transmission train is controlled by means of the linear solenoid valves.
Further, in order to appropriately buffer, by the accumulator, the pressure decrease of the oil pressure in the hydraulic engaging element for the first speed transmission train without giving rise to a speed change shock, it is desirable to control, by pressure regulating means, the oil pressure to be inputted into a back pressure chamber of the accumulator (accumulator back pressure) depending on the running (or operating) conditions of the vehicle. In this case, preferably, the control apparatus further comprises a changeover valve which, when the switching means is controlled to the state in which the oil pressure in the hydraulic engaging element for the first speed transmission train is controllable by said one linear solenoid valve, disconnects a connection between the back pressure chamber of the accumulator and the pressure regulating means to thereby connect the back pressure chamber to a line-pressure oil passage which is in communication with a hydraulic oil pressure source. The oil pressure in the hydraulic engaging element for the first speed transmission train can thus be advantageously controlled in an adequate manner by said one linear solenoid valve without being adversely affected by the accumulator.
In the embodiment to be described in more derail hereinafter, what corresponds to the above-described first control means for speed changing is the processing in the steps S5, S8, S9, S12-S14 in FIG. 7. What corresponds to the above-described second control means for speed changing is the processing in steps S7 and S11 in FIG. 7. What corresponds to the above-described third control means for speed changing is the processing in the step S4 in FIG. 7. What corresponds to the above-described detecting means is the processing of setting a flag FA for discriminating the accumulated pressure shown in FIG. 8. What corresponds to the above-described prohibiting means is the processing in steps S6 and S10 in FIG. 7.